The present invention relates to electronic musical apparatus and, in particular, to an apparatus and circuit which produces a tone having a frequency which is a function of the value of a resistance selected by an operator.
In the past, varying frequencies have been generated by a speaker as powered by an electronic circuit by varying one of the resistance values in the circuit. Various means have been provided for varying that resistance. For example, in some apparatus, pressure sensitive devices have been provided whereby the resistance increases and decreases as a physical pressure is exerted against the device. Two such pressure sensitive devices are disclosed in U.S. Pat. Nos. 2,375,178 and 3,386,067.
In U.S. Pat. No. 3,662,641, variable resistors were also used for tuning an electronic instrument. However, many such variable resistors were required, one for each frequency to be generated. Furthermore, the variable resistors were conventional potentiometers which were not used to select a frequency but rather to assure that a frequency selected by other means was correct and not flat or sharp.
Still another method of varying the resistance has been to provide discrete conductive frets along the neck of a musical instrument with the frets being electronically connected to a resistance ladder. In such an arrangement, an electrical connection at any fret causes a different resistance to be inserted into the circuit thus causing a different frequency to be generated by the instrument. However, such circuits are discrete in nature and require a number of individual discrete resistors connected in a ladder or series configuration and do not incorporate individual variable resistors.
By contrast, the present invention incorporates a single resistor strip for each tone to be simultaneously produced, the resistor strip having a continuous contact surface and a resistance value which is proportional to the length of the strip. The resistor strip is spaced apart from a conductor strip so that by depressing the conductor strip at an appropriate location, contact is made with the continuous contact surface of one or more of the resistor strips thereby inserting different values of resistance into one or more tone generating circuits. Each tone generating circuit generates a signal having a frequency which depends upon that resistance value.
In U.S. Pat. No. 3,626,350, filed February 17, 1970, by Suzuki, et al, a variable resistor device for electronic musical instruments was disclosed incorporating a plurality of strip-shaped resistor bodies formed on one surface of the base member with a resilient pressure contact member covering the resistor bodies. A plurality of mutually spaced apart strips of metal are mounted on the inner surface of the pressure contact member to confront the resistor bodies in spaced relationship. By continuously varying the point of contact between the resistor body and the metal strip, a Portamento chord is produced.
By contrast, the present invention utilizes only a single conductor strip which is spaced over one or more resistor strips in a continuous manner. In addition, the present invention utilizes an insulating fret strip positioned between the conductor strip and the one or more resistor strips to prevent contact between the conductor strip and a particular resistor strip even when the conductor strip is depressed. Discrete tones are then produced by the tone generating circuits by providing holes or spaces in the insulating fret strip so that electrical contact may be made only at discrete locations corresponding to the holes or spaces through the insulating fret strip. Of course, it will be appreciated that the insulating fret strip may be either a single insulating fret strip positioned over the one or more resistor strips or may be a plurality of insulating fret strips, one being provided for each resistor strip.
Thus, the above arrangement provides a simplified variable resistor device for an electrical musical instrument which produces a tone at discrete selected values of frequency.
In still another prior art Patent, No. 2,141,231, issued December 27, 1938, to Trautwein, there is disclosed an electrical musical instrument incorporating a continuous contact bar. However, no insulating fret strip is required or disclosed as a means of selecting the discrete frequencies to be generated by the tone generation circuits. In addition, the above patent incorporates substantially more complex circuitry than the present invention.
Various other related patents were found and cited in the prosecution of Patent No. 3,626,350 discussed above and include U.S. Pat. Nos. 1,847,119; 1,683,059; 2,430,989 and 2,510,792.